To brake a motor vehicle, the wheels of the motor vehicle are braked. In trucks in particular, brake cylinders of the wheels are actuated, wherein the necessary brake pressure is usually generated pneumatically. If the driver of the vehicle requests a braking via a brake pedal, in normal braking mode, the brake pressure is set depending on the driver brake request. As an alternative to normal braking mode, the brake pressure is set by a control unit at the respective wheel brakes and according to the specification from the control unit. DE 10 2009 058 154 A1 discloses a brake system, the control unit of which sets the necessary brake pressures in pressure control mode when braking needs are established. Such braking needs may for example be antilock braking interventions if a braking need is established at specific wheels. The known brake system also takes into account external brake requests, for example from an external driver assistance system. For example, the driver assistance system emits external brake request signals to the control unit via a databus of the vehicle. The control unit sends a resulting brake pressure to the respective wheel brakes taking into account the external brake request and the driver brake request. If the control unit receives an external brake request, and at the same time a driver brake request is made by the driver of the motor vehicle, the control unit of the known brake system overlays the driver brake request and the external brake request, so that the external brake request is implemented additionally or additively. Alternatively, in the known brake system, in a “maximum” mode, the control unit forms only the maximum value of the target deceleration values already requested internally by the brake system and the external target deceleration values, wherein the external brake request is set only if it is higher than the internal brake request. By linking the external brake request and the driver brake request into a resulting brake pressure, it is ensured that an external brake request is activated in pressure control mode even in the absence of a driver brake request.
When the control unit no longer receives an external brake request, or if the driver assistance system revokes the brake request, the known brake system terminates the pressure control mode and returns full control of the brakes to the driver in normal braking mode. In practical driving mode, at the moment of return to normal braking mode when control is restored to the driver, very often an unpleasant jerking of the vehicle occurs, or in other cases a sudden under-braking. Such inconsistencies in the braking behaviour of the motor vehicle often unsettle the driver, and may therefore be a source of danger to the safety of the motor vehicle in road traffic.